A variety of tools are known from the prior art for machining, such as for cutting or milling a tubular or round-bar type piece, or beveling the same at its end. One exemplary tool of the prior art is the angle grinder, comprising a rotating disc for cutting a piece. The rotating disc can also be used for beveling the end of a piece.
However, a problem with such tools is for example how to produce a straight cutting result across the entire pipe, i.e. such that, as the cutting tool is advanced along the pipe surface, how to coincide the finishing point exactly with the starting point without the operator having to make any corrective actions for example towards the very end, thus producing a bend in the cutting line. Another problem with prior known devices is the absence of support, making both cutting and beveling particularly inconvenient. Often, the cutting point or beveling result is not smooth, thus resulting in a possible leakage point for example in the pipe system, either by its raggedness or with sharp cutting edges damaging pipe seals in the process of installing a pipe.
The prior art also discloses devices, seeking to eliminate some of the above-mentioned problems. For example, the Applicant's own patent publication FI 118076 B describes an apparatus, wherein the apparatus includes a clamping mechanism adapted to be fastened to said workpiece rotatably therearound. The clamping mechanism particularly includes a frame element and first and second arms extending therefrom, said arms being articulated at one end to the frame element of the clamping mechanism and each arm having its free end fitted with a bearing axle which is provided with at least one bearing wheel for contact with the surface of a workpiece. The clamping mechanism can be tightened around a piece of circular cross-section by means of said devices. Said apparatus has worked excellently with small and even medium-size pipe dimensions and especially with major resultant cutting forces, whereby the clamping mechanism has retained the machining unit stationary in lateral direction, thus enabling for example the production of a straight cutting result. A problem is nevertheless encountered with large pipe dimensions, because in the process of machining a piece of large dimensions, the arms extending around the piece must have their articulations, by which the arms attach to the clamping mechanism's frame element, spaced from each other at least by a distance that matches the diameter of the piece. What this entails is that, when machining for example a piece 1000 mm in diameter, the clamping mechanism's frame must have a length somewhat in excess of 1000 mm, whereby the apparatus becomes quite bulky and heavy, and hence awkward to operate, as well as often also hazardous as the apparatus is no longer good for steady manual handling. Indeed, it has been an alternative in the prior art to employ equipment of various sizes for pieces of various diameters, which is of course expensive as it requires at least two or three pieces of equipment in varying sizes.
Also, on the other hand, when machining thin-walled pieces, such as for example a thin-walled spiral welded pipe, the clamping mechanisms fastening around a piece may compress the piece and thereby change its shape, whereby producing a straight cutting result becomes difficult or even impossible.
Furthermore, in prior art equipment, the adjustment of a machining or cutting depth to optimal is a difficult operation.